JP4912245B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to a liquid crystal display device having a liquid crystal layer.

  If the storage capacity of the portable information device increases or the communication speed increases, image information with a larger amount of data can be handled. As a result, display devices that are interfaces are required to have higher image quality and higher definition than ever. More specifically, regarding high image quality, high contrast, high color reproducibility, wide viewing angle, and outdoor visibility can be mentioned.

  Since portable information devices are portable, they may be used in various environments with extremely different illuminances. For example, the limit of high illuminance is under direct sunlight in midsummer, and the limit of low illuminance is a dark room. In order to obtain a good display in all of these, a transflective liquid crystal display device is suitable.

  An IPS (In-Plane Switching) liquid crystal display device is characterized by a transmissive display with a wide viewing angle and a high contrast ratio, and a transflective IPS liquid crystal display device in which this is a transflective type has been proposed. A reflection plate for reflecting incident light from the outside is disposed in the reflective display portion of the transflective IPS liquid crystal display device, and a diffuse reflection plate having minute irregularities on the surface is used (Patent Document 1). ). The diffuse reflector reflects the macro-reflecting surface with different incident angles and outgoing angles, and this is called diffuse reflection. On the other hand, a specular reflection plate with a flat reflection surface exhibits regular reflection with the same incident angle and emission angle with respect to a macro reflection surface, and this is called specular reflection.

  With a specular reflector, the amount of light reaching the observer changes rapidly with changes in the positional relationship between the light source and the observer, and good visibility cannot be obtained. On the other hand, the diffuse reflection plate has little change as described above, and high quality visibility like paper can be obtained. In many cases, the observer observes the transflective liquid crystal display device from the normal direction, but the light source is in a direction away from the normal direction. At this time, even if the light source light is specularly reflected, it does not reach the observer, so a sufficient amount of light cannot be obtained with the specular reflector, and diffuse reflection is necessary to increase the amount of light reaching the observer, and therefore diffusion A reflector is required. As described above, since the diffuse reflector has minute irregularities on the surface and is close to the liquid crystal layer, the liquid crystal layer tends to be thicker at the concave portion of the diffuse reflector, and the liquid crystal layer becomes thinner at the convex portion. There is a tendency. Thus, the diffusive reflector causes local fluctuations in the thickness of the liquid crystal layer.

JP 2000-338520 A

  In a liquid crystal display device, an electric field is applied to a liquid crystal layer using two electrodes, and among these, a pixel electrode is applied with a potential corresponding to image information for each pixel, and a common electrode is applied between pixels. Call. In the IPS liquid crystal display device, at least one of the pixel electrode and the common electrode has a comb-like shape, and electric lines of force are distributed in an arched arc in the liquid crystal layer so as to connect the pixel electrode and the common electrode. Since the direction of the electric lines of force and the electric field strength are different in each part of the arch-shaped electric lines of force, the alignment state of the liquid crystal when the electric field is applied becomes nonuniform. Since uniform liquid crystal alignment can be obtained only when no voltage is applied, it is necessary to make dark display when no voltage is applied, and to be a normally-closed applied voltage dependency in which transmittance or reflectance increases with voltage application.

  In a reflective liquid crystal display device using a polarizing plate, dark display is obtained by making the polarization state of light reaching the reflector plate circularly polarized. That is, at this time, the polarization state of the transmitted light is linearly polarized light after passing through the polarizing plate, but when this light is reflected by the reflector and reaches the polarizing plate again, it becomes linearly polarized light whose polarization direction is rotated by 90 degrees, This is because it is completely absorbed by the polarizing plate. This applies to all transflective liquid crystal display devices including transflective IPS liquid crystal display devices.

  A phase plate is disposed between the liquid crystal layer and the polarizing plate. To realize circularly polarized light, the combined value of Δnd (birefringence × layer thickness) of the liquid crystal layer and the phase plate must be a quarter wavelength. When no voltage is applied, the liquid crystal layer of the IPS mode liquid crystal display device is homogeneously aligned, and the apparent Δn of the liquid crystal layer does not become 0 nm. Therefore, Δnd does not become 0 nm but takes a certain value. As described above, since the diffusive reflecting plate locally varies the thickness of the liquid crystal layer, Δnd also varies. If Δnd of the liquid crystal layer varies from a predetermined design value, the polarization state of the light reaching the reflection plate also becomes a polarization state different from the circular polarization, and the reflectance during dark display increases. If the reflectance during dark display increases, the contrast ratio of the reflective display decreases and a good reflective display cannot be obtained.

  In order to prevent a reduction in contrast ratio, the height of the unevenness of the diffuse reflector should be lowered. On the other hand, the diffusion characteristics of the diffuse reflector depend on the height of the unevenness and the pitch of the unevenness (the average distance between the recesses and the protrusions). If the height of the unevenness is reduced while keeping the pitch of the unevenness constant, the diffuse reflector has a reflection characteristic close to that of the specular reflector, and sufficient diffuse reflection cannot be obtained. It is necessary to reduce the height of the unevenness while keeping the ratio of the height of the unevenness and the pitch of the unevenness constant. However, there are cases where the height of the unevenness cannot be sufficiently reduced due to restrictions on processing process accuracy. Therefore, when the conventional technique is used, it is difficult to achieve both the contrast ratio and the diffusion characteristics.

  An object of the present invention is to provide a liquid crystal display device capable of reducing the reflectance in dark display, improving the contrast ratio of the reflective display, and maintaining good diffusibility.

  In order to solve the above problems, the present invention provides a pair of substrates, a liquid crystal layer sandwiched between the pair of substrates, a plurality of pixels, a reflective display unit and a transmissive display unit in each pixel of the plurality of pixels. And between one substrate of the pair of substrates and the liquid crystal layer are formed at the intersection of the plurality of signal lines, the plurality of scanning lines formed to intersect the plurality of signal lines, and the signal lines and the scanning lines. The formed active element, the pixel electrode, the common electrode, and the diffuse reflection portion formed at a position corresponding to the reflective display portion are formed, and the diffuse reflection portion is a concavo-convex forming layer in which a concave portion and a convex portion are formed. And a common electrode formed on the concave portion of the concave-convex forming layer, and a reflective layer formed on the convex portion of the concave-convex forming layer and the common electrode.

  Further, the display device includes a pair of substrates, a liquid crystal layer sandwiched between the pair of substrates, a plurality of pixels, and a reflective display portion and a transmissive display portion in each pixel of the plurality of pixels. Between the substrate and the liquid crystal layer, a plurality of signal wirings, a plurality of scanning wirings formed to cross the plurality of signal wirings, an active element formed at an intersection of the signal wirings and the scanning wirings, a pixel electrode, A common electrode and a diffuse reflection part formed at a position corresponding to the reflective display part are formed, and the diffuse reflection part is formed on the concave / convex forming layer on which the concave part and the convex part are formed, and on the concave / convex forming layer The reflective layer and the common electrode formed on the concave portion of the reflective layer are used.

  In addition, the display device includes a pair of substrates, a liquid crystal layer sandwiched between the pair of substrates, a plurality of pixels, and a reflective display portion and a transmissive display portion in each pixel of the plurality of pixels. The layers include a plurality of signal lines, a plurality of scanning lines formed to intersect the plurality of signal lines, an active element formed at the intersection of the signal lines and the scanning lines, a pixel electrode, and a reflective display unit. A diffusive reflecting portion formed at a position corresponding to the substrate, a common electrode is formed between the other substrate of the pair of substrates and the liquid crystal layer, and the diffusing reflective portion is a concavo-convex forming layer in which concave portions and convex portions are formed. And a pixel electrode formed on the concave portion of the concave-convex forming layer, and a reflective layer formed on the convex portion of the concave-convex forming layer and the pixel electrode.

  It is possible to provide a liquid crystal display device capable of reducing the reflectance in display, improving the contrast ratio of the reflective display, and maintaining good diffusibility.

  Embodiments will be described below with reference to the drawings.

  A cross section of one pixel of the liquid crystal display device of the present invention is schematically shown in FIGS. Each cut surface is described in FIG. The liquid crystal display panel includes a first substrate SU1, a second substrate SU2, and a liquid crystal layer LCL. The first substrate SU1 and the second substrate SU2 sandwich the liquid crystal layer LCL. The first substrate SU1 and the second substrate SU2 are alignment films (first alignment film AL1, second alignment film AL2) for stabilizing the alignment state of the liquid crystal layer LCL on the surface close to the liquid crystal layer LCL. Is provided. Further, a means for applying a voltage to the liquid crystal layer LCL is provided on the surface of the second substrate SU2 that is close to the liquid crystal layer LCL. Further, as shown in FIG. 1, one pixel is divided into a transmissive display portion and a reflective display portion in terms of area. FIG. 3 and FIG. 4A are cross sections of the transmissive display unit and the reflective display unit, respectively.

  The first substrate SU1 is made of borosilicate glass that is excellent in transparency and flatness and contains little ionic impurities, and has a thickness of about 400 μm. The first substrate SU1 includes a first alignment film AL1, a step forming layer ML, a protective layer PL, a retardation layer RE, a retardation film alignment film ALP, a planarization layer LL, and a color filter CF from the side close to the liquid crystal layer LCL. , And black matrix BM are sequentially stacked. The first alignment film AL1 and the retardation film alignment film ALP are polyimide-based organic polymer films, which are aligned by a rubbing method, so-called horizontal that gives a pretilt angle of about 2 degrees to the adjacent liquid crystal layer LCL. It is an alignment film. The protective layer PL and the flattening layer LL are acrylic resins, have excellent transparency, and have a function of flattening the unevenness of the base and preventing permeation of the solvent. The step forming layer ML is an acrylic resin like the protective layer PL and the planarizing layer LL, and is distributed only in a portion corresponding to the reflective display portion. The color filter has a planar structure in which striped portions exhibiting red, green, and blue are repeatedly arranged. The black matrix is made of a black resist and has a lattice-like planar distribution structure so as to correspond to the pixel boundary portion.

  Like the first substrate SU1, the second substrate SU2 is made of borosilicate glass and has a thickness of about 400 μm. The second substrate SU2 mainly includes a second alignment film AL2, a pixel electrode PE, an interlayer insulating film PCIL, a common electrode CE, an active element, a scanning line GL, and a signal line SL in order from the side close to the liquid crystal layer LCL. . Similar to the first alignment film AL1, the second alignment film AL2 is a horizontal alignment film made of a polyimide organic polymer film. The pixel electrode PE and the common electrode CE are both indium tin oxide (ITO) having both transparency and conductivity, and the layer thickness is 100 nm. Both are separated by an interlayer insulating film PCIL made of silicon nitride (SiN), and the thickness of the interlayer insulating film PCIL is 300 nm. The planar shape of the pixel electrode PE is comb-shaped, whereas the common electrode CE has a common electrode hole portion CEH as described later, but is distributed over almost the entire surface of each pixel. Since the pixel electrode PE and the common electrode CE are separated from each other by the interlayer insulating film PCIL, an arch-shaped electric field line is formed between the two when the voltage is applied. This is a so-called lateral electric field having a component parallel to the substrate plane, and is an IPS liquid crystal display panel in which the alignment state of the liquid crystal layer LCL is mainly deformed so as to rotate in the plane.

  In the IPS liquid crystal display panel, the increase in tilt angle of the liquid crystal layer due to voltage application is small, so that a wide viewing angle display excellent in gradation display characteristics in the viewing angle direction can be obtained. Further, in FIG. 1, there are many portions where the pixel electrode and the common electrode overlap each other, but since this portion is coupled in parallel to the liquid crystal layer, it functions as a holding capacitor that keeps the applied voltage constant during the holding period. .

  In addition, the reflective display portion of the second substrate SU2 includes a reflective layer (reflective electrode RF) above the common electrode CE. In addition, a concavo-convex forming layer SCIL is provided below the common electrode CE, and the concavo-convex forming layer SCIL has a large number of minute and gentle concavo-convex portions in a portion overlapping the reflective layer. The concavo-convex forming layer SCIL is made of an organic insulating film, and the surface of the organic insulating film is etched and then heated to a molten state. The surface tension at this time is used to make the surface smooth and uneven, and this is solidified to form the unevenness. Since the reflective electrode RF of the reflective layer on the upper surface of the concavo-convex forming layer SCIL has a shape along the concavo-convex forming layer SCIL, the reflective layer has a large number of minute planes inclined with respect to the macroscopic layer plane, and is diffusely reflected. Indicates. When the relationship between the light source and the viewing direction changes, the specular reflection plate changes rapidly, which is not preferable for visual recognition. Even if the relationship between the light source and the viewing direction changes, the diffuse reflector has little change in reflected luminance, and a high-quality reflective display surface close to a perfect diffuse surface can be obtained. The reflective layer is an aluminum film exhibiting a high reflectivity, and a molybdenum film is interposed between the reflective layer and the common electrode so as to have the same potential.

  Focusing on the convex portions in the planar structure of the concave-convex forming layer SCIL, if the convex portions are more densely distributed, the area ratio of the flat portions is reduced and the ratio of diffuse reflection is increased. For example, if the convex portions are formed in a circular shape and are arranged in the closest density, the convex portions can be distributed most densely. FIG. 7A is a plan view showing the distribution of convex portions in this state, and FIG. 7A corresponds to contour lines in the concavo-convex forming layer SCIL. The inner side of the circle shown in FIG. 7A is a convex portion, which is higher than the surrounding area.

  However, as shown in FIG. 7A, when the distribution of the convex portions is regular, an interference effect occurs in the reflected light, and the reflected light is colored. Coloring due to the interference effect is not preferable for visual recognition because it shows a striped color distribution and the color distribution changes rapidly as the viewing direction changes. In order to reduce the interference effect while maintaining sufficient diffuse reflection, it is only necessary to randomly shift the individual protrusions from the close-packed arrangement. In other words, the distance to be shifted may be determined at random while the maximum value is about half or less of the distance of the convex portion in the closest densely arranged arrangement, and the direction to be shifted may be determined at random.

  At this time, as shown in FIG. 7B, the two convex portions overlap each other, and the area ratio of the flat portion increases. Therefore, as shown in FIG. 7C, if the overlapping convex portions are connected and the area of the convex portions whose periphery is sparse is increased, an increase in the area ratio of the flat portion can be suppressed. Alternatively, the shape of the convex portion may be appropriately changed to an ellipsoid or a polygon in consideration of the positional relationship with the adjacent convex portion.

  In the reflective display portion, the common electrode CE has a plurality of common electrode hole portions CEH. The distribution of the common electrode hole part CEH and the convex part is shown in FIG. As shown by a broken line in FIG. 7D, the common electrode hole part CEH is distributed so as to correspond to the convex part CONV of the concave-convex forming layer SCIL, and as a result, in a portion overlapping with the concave-convex forming layer. The common electrodes are distributed so as to correspond to the concave portions of the concave-convex forming layer. The difference in height between the concave portion and the convex portion due to the concave / convex formation layer SCIL is reduced by the thickness of the common electrode CE. Further, the common electrode CE has no flattening effect and its thickness is uniform. Although the reflective layer is laminated on the concavo-convex forming layer SCIL and the common electrode CE, the angle distribution of the micro-plane of the reflective layer is the same as when the common electrode hole portion CEH does not exist, and the light diffusivity is also common electrode empty. This is the same as when no hole CEH is present.

  An interlayer insulating film PCIL and a pixel electrode PE are provided above the reflective layer. The interlayer insulating film PCIL is made of silicon nitride and the pixel electrode PE is made of indium tin oxide, and both have no flattening effect. Further, as will be described later, a second alignment film AL2 exists above and is in contact with the liquid crystal layer. However, since the layer thickness is thin, there is almost no flattening effect. However, since the difference in height between the concave and convex portions of the concave / convex forming layer is reduced by the common electrode hole portion CEH, the local layer thickness variation applied to the reflective portion liquid crystal layer does not have the common electrode hole portion CEH. Decrease compared to the case. The common electrode CE needs to be removed around the contact hole in order to insulate it from the pixel electrode PE, but the common electrode hole portion CEH can be formed at the same time. Therefore, the common electrode hole portion CEH can be formed without increasing the number of manufacturing steps.

  As shown in FIG. 2, the signal line SL and the scanning line GL intersect each other. Active elements are provided in the vicinity of the intersections between the signal lines and the scanning lines, and correspond to the pixel electrodes PE on a one-to-one basis. A potential is applied to the pixel electrode PE from the signal wiring through the active element, and the operation of the active element is controlled by the scanning wiring. The active element is a thin film transistor, and its channel portion is made of a polysilicon layer having a relatively high electron mobility. The polysilicon layer is formed by heating and baking an amorphous silicon layer formed by a CVD (Chemical Vapor Deposition) method with a laser beam. Each pixel electrode is rectangular and controlled independently of each other, and is arranged in a grid pattern on the second substrate SU2.

  In the transmissive display portion, the light passes through the color filter CF only once, whereas in the reflective display portion, the light passes through the color filter CF because it is reflected by the reflecting plate. Therefore, if the same color filter CF is used for the reflective display portion and the transmissive display portion, the effective transmittance is lowered in the latter case. Furthermore, since the reflective display unit uses incident light from the outside as a light source, a bright display cannot be obtained if the surroundings are not sufficiently bright. In order to obtain a bright reflective display under a wider range of environments, the color filter of the reflective display unit has a higher transmittance than the transmissive display unit.

  Specifically, as shown in FIG. 5, a color filter hole portion CFH in which the color filter CF does not exist is arranged in the reflection display portion, and reflection display is performed by additive color mixing with the hole portion. Here, FIG. 5 is a plan view of the first substrate SU1, and shows a planar distribution of the color filter CF and the black matrix BM of the liquid crystal display device of the present embodiment. FIG. 5 includes a region corresponding to three pixels, and is a red, green, and blue color filter from the left side. Alternatively, the same effect can be obtained by reducing the thickness of the color filter of the reflective display portion.

  FIG. 6 is a plan view of the first substrate as in FIG. 5, but shows a planar distribution of the retardation layer RE in addition to the color filter CF and the black matrix BM. In order to show the planar distribution of the phase difference layer RE, the black matrix BM is shown as white but different from the actual one. The retardation layer RE is distributed in stripes so as to connect the reflective display portions of the respective pixels.

  The liquid crystal layer LCL exhibits a nematic phase in a wide temperature range including room temperature, and exhibits positive dielectric anisotropy in which the dielectric constant in the liquid crystal alignment direction is larger than that in the vertical direction. In addition, since the liquid crystal layer LCL exhibits high resistance, the voltage drop is sufficiently small even during the holding period in which the active element is turned off, and the transmittance reduction and the so-called flicker phenomenon do not occur during the holding period. After the first alignment film AL1 and the second alignment film AL2 are subjected to alignment treatment by a rubbing method, the first substrate and the second substrate are assembled, and a liquid crystal material is vacuum-encapsulated to form the liquid crystal layer LCL described above. .

  By making the alignment treatment directions of the first alignment film AL1 and the second alignment film AL2 antiparallel, the liquid crystal layer LCL is made homogeneous alignment with a stable alignment state. The orientation direction is 10 degrees with respect to the comb-tooth direction of the signal electrode, and 80 degrees with respect to the transverse electric field generated when a voltage is applied. Thereby, a sufficiently large change in the orientation of the liquid crystal layer can be obtained when a voltage is applied. In addition, the direction of orientation change when a voltage is applied, that is, the rotation direction (clockwise or counterclockwise) of the liquid crystal layer in the layer is uniquely determined, and a stable orientation change can be obtained.

  A first polarizing plate PL1 and a second polarizing plate PL2 are arranged outside the first substrate SU1 and the second substrate SU2, and the first polarizing plate PL1 and the second polarizing plate PL2 are iodine-based. It contains a pigment and iodine forms a multimer in the polarizing plate. Due to the dichroism, the polarizing plate converts incident natural light into linearly polarized light having a sufficiently high degree of polarization. The orientation direction of the iodine dye multimer is the absorption axis, and the absorption axes of the first polarizing plate PL1 and the second polarizing plate PL2 are orthogonal to each other when observed from the plane normal direction. The absorption axis of the plate PL1 is parallel to the liquid crystal alignment direction.

  FIG. 8 is a schematic diagram showing the formation process of the retardation layer RE, and describes the S9-S10 cross section shown in FIG. In FIG. 8, the color filter CF and the planarization layer LL on the first substrate SU1 are omitted. FIG. 8A shows a state in which the retardation film alignment film ALP is aligned by rubbing. As shown in FIG. 8B, the retardation layer RE is aligned with the retardation film alignment film ALP. Homogeneous orientation along the direction. The material for the retardation layer RE is a diacrylic liquid crystal mixture, which is dissolved in an organic solvent together with a photoreaction initiator and applied onto the retardation film alignment film ALP by means such as spin coating or printing. Although it is in a solution state immediately after coating, it is aligned along the alignment direction of the retardation film alignment film ALP while evaporating the solvent.

  As shown in FIG. 8C, this is irradiated with ultraviolet light to cause a polymerization reaction between acrylic groups at the molecular ends. At this time, oxygen becomes an inhibitory factor for the polymerization reaction, but if the concentration of the photoinitiator is sufficient, the photoreaction proceeds at a sufficient speed. FIG. 8C shows a state in which liquid crystal molecules indicated by ellipses are almost completely bonded. FIG. 8D shows a state developed with an organic solvent, and the retardation layer RE is formed only on the light irradiation portion. As described above, the retardation layer RE is formed by solidifying while maintaining the alignment state in the liquid crystal layer LCL roughly. As shown in FIG. 8E, thereafter, the retardation layer is overheated in each process of forming the RE protective layer PL and forming the first alignment film AL1. Since the decrease in Δnd in the high temperature state is substantially proportional to the length of time in the high temperature state if the temperature in the high temperature state is constant, the initial Δnd is set in consideration of this.

  The retardation layer RE is necessary for the reflective display unit, but is not necessary for the transmissive display unit. If the retardation layer RE is formed in the transmissive display portion, the contrast ratio of the transmissive display is lowered. Therefore, the retardation layer RE is formed only in a portion other than the transmissive display portion on the second substrate SU2. Specifically, only a portion where the retardation layer RE is necessary is irradiated with light using a photomask during light irradiation to solidify. Since the portion not irradiated with light is not solidified, it is removed by washing with an organic solvent or the like. In this case, since the retardation layer RE is physically removed from the transmissive display portion, the influence of the retardation can be completely eliminated. Alternatively, the portion corresponding to the transmissive display portion may be heated to the isotropic liquid crystal mixture to form an isotropic layer, and light is irradiated in this state to solidify the isotropic phase. In this case, an organic development process becomes unnecessary.

  The optical axis directions of the first polarizing plate PL1, the retardation layer RE, and the reflective display portion liquid crystal layer, and Δnd of the retardation layer and the reflective display portion liquid crystal layer are determined in the same manner as in the broadband quarter-wave plate. . The broadband quarter-wave plate has a structure in which a polarizing plate, a half-wave plate, and a quarter-wave plate are sequentially stacked, and is incident polarized in a wider wavelength range of the visible wavelength centered at a wavelength of 550 nm. Has a function of converting the light into circularly polarized light or a polarization state very close to this.

  The principle will be described below using the Poincare sphere display. The Poincare sphere display is described in detail in books such as “Applied Physics Society”, Morikita Publishing “Crystal Optics”, or by Tatsuta Tatsuo and Baifukan “Applied Optics II”. In the following, the Poincare sphere is regarded as the earth, the intersection of the S3 axis and the Poincare sphere is called the North Pole and the South Pole, and the intersection of the S1, S2 plane and the Poincare sphere is called the equator. In this case, the north and south poles represent circularly polarized light, the equator represents linearly polarized light, and the other parts represent elliptically polarized light. The S1, S2, and S3 axes are Stokes parameters in the polarization state, which are values normalized by the Stokes parameter S0 representing the intensity.

  The broadband quarter-wave plate is designed with reference to light having a wavelength of 550 nm that maximizes the visibility. A change in polarization state when light having a wavelength of 550 nm passes through a broadband quarter-wave plate is shown. The light that has passed through the polarizing plate is positioned at one point on the equator because it is linearly polarized light. However, when it enters the half-wave plate, it rotates by a half around the axis corresponding to its slow axis, and on the equator. Move to another point. Next, when the light enters the quarter-wave plate, it rotates by a quarter of the axis corresponding to the slow axis, moves to the north pole, and is converted into circularly polarized light.

  As with most optically anisotropic media, Δnd of the half-wave plate shows a wavelength dependency that monotonously decreases with wavelength in the visible wavelength region. Therefore, on the long wavelength side of the visible wavelength region, the rotation is half or less as shown in FIG. 11B, and moves to the northern hemisphere without reaching the equator. On the short wavelength side of the visible wavelength range, as shown in FIG. 11 (c), the rotation becomes a half or more, and moves on the southern hemisphere through the equator. In the next quarter-wave plate, the moving direction is substantially opposite, and the same wavelength dependency as that of the previous half-wave plate is exhibited. On the long wavelength side of the visible wavelength, as shown in FIG. 11 (b), the distance from the North Pole is closer because the direction is toward the North Pole starting from the Northern Hemisphere, but the rotation at this time is less than a quarter turn. Because it is small, it reaches near the North Pole. On the short wavelength side of the visible wavelength, as shown in FIG. 11 (c), since it goes to the north pole starting from the southern hemisphere, the distance to the north pole is farther, but the rotation is larger than a quarter rotation, so the north pole Reach nearby. In this way, by stacking a half-wave plate and a quarter-wave plate having the same Δnd wavelength dependency in an angular relationship such that the rotation direction on the Poincare sphere is approximately opposite, Δnd Cancels the wavelength dependence of.

In the present invention, since the reflective portion liquid crystal layer and the retardation layer RE are laminated in this order from the side close to the reflective layer, the reflective portion liquid crystal layer corresponds to a quarter-wave plate, and the retardation layer RE is divided into two minutes. This corresponds to a single wave plate. That is, Δnd of the reflective liquid crystal layer may be set to correspond to a quarter-wave plate, and retardation of the retardation layer RE may be set to correspond to a half-wave plate. The angle setting of the optical axis is also derived from FIG. 11A, but for clarity, this is projected on the S1 and S2 planes and shown in FIG. In this case, the center is the north or south pole, and the circumference is the equator. In FIG. 10A, the conversion of the polarization state is represented as a movement that moves counterclockwise in the northern hemisphere of the Poincare sphere and reaches the north pole. In addition to this, as a quarter-wave plate, the Poincare sphere's northern hemisphere moves clockwise to reach the North Pole, the Poincare sphere's southern hemisphere moves counterclockwise to the South Pole, and the Poincare sphere's southern hemisphere rotates clockwise. And moved to reach the South Pole, as shown in FIGS. 10B, 10C, and 10D, respectively. If the slow axis azimuth angle θ _PH of the retardation layer and the alignment direction azimuth angle θ _LC of the liquid crystal layer are respectively defined counterclockwise with the transmission axis azimuth angle of the first polarizing plate as 0 degree, θ _PH and θ _LC The relationship is expressed by the following equation from FIGS.

2θ _PH = ± 45 ° + θ _LC (1)
Note that θ _PH ′ and θ _LC ′ in FIG. 10 are in the relationship of θ _PH , θ _LC and 2θ _PH ′ = θ _PH , 2θ _LC ′ = θ _PH , respectively. Thus, there are many combinations of θ _PH and θ _LC , which are not uniquely determined. However, in the present invention, the alignment direction of the liquid crystal layer LCL is the same between the reflective display portion and the transmissive display portion, and the first polarizing plate PL1 is attached to the outside of the liquid crystal panel. There is a restriction that the display is the same. Therefore, the alignment direction of the reflective liquid crystal layer is parallel or orthogonal to the transmission axis direction of the first polarizing plate PL1. That is, θ _LC = 0 ° or ± 90 °, and considering that the rotation direction on the Poincare sphere is approximately opposite, θ _PH = ± 62.5 ° is eventually obtained.

  As described above, the reflectance of the reflected black display can be reduced most in the combination of the retardation layer RE and the reflective liquid crystal layer. As shown by the solid line in FIG. 9, the reflectance of the reflection spectrum is reduced over a wide visible wavelength range centering on the wavelength of 550 nm. Alternatively, the reflectance can be increased while keeping the dark display reflectance relatively low by increasing the Δnd of the reflection portion liquid crystal layer while keeping the ratio of Δnd between the retardation layer RE and the reflection portion liquid crystal layer approximately.

  The integrating sphere light source was placed on the upper surface of the liquid crystal display device of the present invention with the same distance as the opening radius, and the contrast ratio of the reflective display was measured. Reflective display uses light incident from a direction inclined with respect to the normal direction as a light source, and the display device itself is often observed from the normal direction, but this method reflects the actual usage. Characteristic evaluation becomes possible. The obtained contrast ratio was about 1.6 times that in the case where the common electrode hole layer CEH was not formed on the common electrode CE.

  As described above, by forming the common electrode hole layer CEH so as to correspond to the convex part CONV of the concave / convex forming layer, the angular distribution of the minute plane of the concave / convex forming layer is maintained, and the height of the concave part and the convex part is maintained. The difference is also reduced. This reduces local layer thickness fluctuations applied to the liquid crystal layer, reduces Δnd deviation from an ideal broadband quarter-wave plate, and reduces the increase in dark display reflectance. In addition, the diffusibility of the reflective layer can be maintained. The contrast ratio of the reflective display of the transflective IPS liquid crystal display device could be improved without increasing the manufacturing process.

  In Example 1, as shown in FIG. 4B, the stacking order of the common electrode CE and the reflective electrode RF as the reflective layer was reversed. In this case, since the reflective layer is close to the concavo-convex formation layer SCIL without passing through the common electrode CE, the angle distribution of the micro-plane of the reflective layer is the same as when the common electrode hole portion CEH is not present, and the light diffusibility is also high. This is the same as when no common electrode hole portion exists.

  In the first embodiment, a molybdenum film is interposed between the common electrode CE and the reflective layer so as to have the same potential. However, in this embodiment, when a molybdenum film is formed between the common electrode CE and the reflective layer, the upper layer of the reflective layer is formed. Exposed to. Since the molybdenum film has a lower reflectance than the aluminum film constituting the reflective layer, the reflectance is not preferable. In this embodiment, a molybdenum film is not formed between the common electrode CE and the reflective layer, and power is supplied independently at the end of the display region of the liquid crystal display device in order to make the common electrode CE and the reflective layer have the same potential. .

  Also in this example, the local variation in the layer thickness applied to the liquid crystal layer LCL was reduced, and the diffusibility of the reflective layer could be maintained. The contrast ratio of the reflective display is improved as compared with the case where the common electrode hole layer CEH is not formed on the common electrode CE.

  In this example, a combination of Δnd of the retardation layer RE and the reflective liquid crystal layer that reduces the dark display reflectance was obtained by calculation. The axial angles of the first polarizing plate PL1, the retardation layer RE, and the reflective liquid crystal layer were set to the values in claim 1, and the optical paths at the time of incidence and reflection were assumed to be normal directions. Using a commercially available one-dimensional calculation software that performs optical calculation by the Jones matrix method, the dark display reflectance was calculated while changing the combination of Δnd of the retardation layer RE and the reflective liquid crystal layer. The calculation result is shown in FIG.

  In FIG. 12A, the + mark indicates that Δnd of the retardation layer RE and the reflective liquid crystal layer at the wavelength of 550 nm is an ideal broadband quarter-wave plate value, that is, the former is 275 nm and the latter is 137.5 nm. A region indicated by a solid line is a region in which a dark display reflectance of 1.5 times or less of the value at this time is obtained. The outer broken line, the one-dot chain line, and the dotted line are areas where a dark display reflectance of 2.0 times, 2.5 times, and 3.0 times that of an ideal broadband quarter-wave plate can be obtained. As described above, the region where a good dark display reflectance is obtained is distributed in an approximately elliptical shape with the + mark as the center. The region is an ellipse whose major axis is inclined, and its inclination is positive. If a proportional relationship is established between Δnd of the retardation layer RE and the reflective liquid crystal layer, the dark display reflectance can be reduced.

From this, a straight line corresponding to the major axis of the ellipse was extracted, and the relational expression was obtained as shown in FIG. Assuming that Δnd of the retardation layer is Δnd _PH and Δnd _LC of the liquid crystal layer of the reflective display section is Δnd _LC , Δnd _PH and Δnd _LC are Δnd _PH = 1.37 Δnd _LC +86 or both in the vicinity thereof. Even if Δnd deviates from the ideal broadband quarter-wave plate value, a relatively good dark display reflectance can be obtained.

  This can be explained qualitatively using FIGS. 11B and 11C. That is, when Δnd of the retardation layer is smaller than the ideal value, if Δnd of the reflective liquid crystal layer is also smaller than the ideal value, it can move to the vicinity of the Poincare sphere, and the dark display reflectance can be reduced. Conversely, when Δnd of the retardation layer is larger than the ideal value, it can be moved to the vicinity of the Poincare sphere if Δnd of the liquid crystal layer of the reflecting portion is larger than the ideal value.

  The above results are effective for determining the Δnd of the retardation layer when the reflectance is given priority and the Δnd of the liquid crystal layer of the reflective display portion is set larger than the ideal quarter-wave plate value. It is.

  On the other hand, in Example 1, the common electrode hole portion CEH was not formed. In this case, the difference in height between the concave and convex portions of the concave / convex forming layer was not reduced, and the local variation in the layer thickness applied to the liquid crystal layer was also not reduced. Therefore, the contrast ratio of the reflective display is lower than that in Example 1.

  In this embodiment, the present invention is applied to a vertical electric field type transflective liquid crystal display device driven by applying an electric field in the thickness direction of the liquid crystal layer LCL. FIG. 13 shows a cross section of one pixel of the liquid crystal display device of this example. FIG. 13 is a cross section taken along S1-S2 in FIG.

  The common electrode CE was formed on the first substrate SU1, and the pixel electrode PE was formed in a flat plate shape so as to be close to the reflective electrode RF. Accordingly, the interlayer insulating film PCIL is removed, and further, the retardation film alignment film ALP, the retardation layer RE, and the protective layer PL are removed. Further, the pixel electrodes PE were patterned so as to be distributed only in the concave portions of the concave / convex forming layer of the diffuse reflector. Other than that, it is the same as the embodiment described above.

  That is, in this embodiment, a pair of substrates (first substrate SU1, second substrate SU2), a liquid crystal layer LCL sandwiched between the pair of substrates, a plurality of pixels, and in each pixel Between the second substrate SU2, which is one substrate of the pair of substrates, and the liquid crystal layer LCL, the plurality of signal lines SL and the plurality of signal lines SL are crossed. A plurality of scanning lines GL formed, TFTs that are active elements formed at intersections of the signal lines SL and the scanning lines GL, pixel electrodes PE, and diffuse reflection formed at positions corresponding to the reflective display section The common electrode CE is formed between the first substrate SU1, which is the other substrate, and the liquid crystal layer LCL.

  FIG. 14 shows a cross section of the reflective display portion of the liquid crystal display device of this example. FIG. 14 is a cross section taken along line S5-S6 of FIG. By distributing the pixel electrode PE only in the concave portions of the concave-convex forming layer, fluctuations given to the liquid crystal layer LCL thickness were reduced.

  As a characteristic structure of this embodiment, the diffuse reflection portion includes a concavo-convex forming layer SCIL in which concave and convex portions are formed, a pixel electrode PE formed on the concave portion of the concavo-convex forming layer SCIL, and a concavo-convex forming layer SCIL. A reflective electrode RF that is a reflective layer formed on the convex portion and the pixel electrode PE, and the effect thereof is the same as that of the first embodiment.

  In the present embodiment, the first outer retardation layer ORE1 is disposed between the first substrate SU1 and the first polarizing plate PL1, and the second substrate SU2 and the second polarizing plate PL2 are arranged between the first substrate SU1 and the first polarizing plate PL2. Two outer retardation layers ORE2 were disposed. The first outer retardation layer ORE1 and the second outer retardation layer ORE2 are both arranged so as to be distributed in both the reflective display portion and the transmissive display portion.

  In order to make the reflective display and transmissive display dependent on the normally closed type applied voltage by vertical electric field driving, the absorption axis of the first polarizing plate PL1, the absorption axis of the second polarizing plate PL2, and the alignment state of the liquid crystal layer LCL , Δnd was changed. The liquid crystal display device was observed from the normal direction in the state of use, and the horizontal direction at this time was defined as an azimuth angle of 0 degrees and increasing counterclockwise. The absorption axis azimuth angles of the first polarizing plate PL1 and the second polarizing plate PL2 were 140 degrees and 55 degrees, respectively. The slow axis azimuth of the first outer retardation layer ORE1 was 125 degrees, Δnd at a wavelength of 550 nm was 400 nm, and the Nz coefficient was 0. The slow axis azimuth of the second outer retardation layer PLE2 was 170 degrees, Δnd at a wavelength of 550 nm was 185 nm, and the Nz coefficient was 1.

  For the liquid crystal layer LCL, a liquid crystal material exhibiting a nematic phase in a wide temperature range including room temperature was used, and Δn was set to 0.072. The alignment process direction of the first alignment film PL1 and the second alignment film PL2 is set to 20 degrees and 250 degrees, respectively, and a chiral agent that induces spontaneous twisting is added to the liquid crystal layer LCL to add a liquid crystal layer The LCL was twisted with a twist angle of 50 degrees. The thickness of the step forming layer ML was adjusted so that the liquid crystal layer thicknesses in the transmissive display portion and the reflective display portion were 5.1 μm and 3.6 μm, respectively.

  In the case of this embodiment, the liquid crystal layer of the reflective display portion has Δnd of about 260 nm when no voltage is applied for performing dark display. However, the variation in Δnd is caused by the reduction in local layer thickness variation applied to the liquid crystal layer. Could also be reduced. In addition, the diffusibility of the reflective layer could be maintained. Thereby, the contrast ratio of the reflective display can be improved as compared with the case where the common electrode hole layer is not formed on the common electrode CE.

It is sectional drawing of one pixel of the liquid crystal display device of Example 1. It is a top view which shows the structure on the 2nd board | substrate of the liquid crystal display device of Example 1. FIG. It is sectional drawing of the transmissive display part of the liquid crystal display device of Example 1. FIG. It is sectional drawing of the reflective display part of the liquid crystal display device of Example 1 and Example 2. FIG. It is a top view which shows the structure on the 1st board | substrate of the liquid crystal display device of Example 1. FIG. It is a top view which shows the structure on the 1st board | substrate of the liquid crystal display device of Example 1. FIG. It is a top view which shows distribution of the convex part of an uneven | corrugated formation layer, and a common electrode hole part. It is a figure showing the formation process of the phase difference layer of Example 1. FIG. It is a figure showing the reflection spectrum at the time of the dark display of the reflective display part of the liquid crystal display device of Example 1. FIG. It is a figure showing conversion of the polarization state of incident light at the time of dark display by a phase contrast layer and a reflection part liquid crystal layer. It is a figure showing conversion of the polarization state of incident light at the time of dark display by a phase contrast layer and a reflection part liquid crystal layer. It is a figure which shows the retardation relationship of the phase difference layer and reflective part liquid crystal layer which reduce a dark display reflectance. It is sectional drawing of one pixel of the liquid crystal display device of Example 4. It is sectional drawing of the reflective display part of the liquid crystal display device of Example 4.

Explanation of symbols

PL1 first polarizing plate
PL2 Second polarizing plate SU1 First substrate SU2 Second substrate LL Flattening layer AL1 First alignment film LCL Liquid crystal layer AL2 Second alignment film GL Scanning wiring CF Color filter BM Black matrix RE Phase difference layer ML Step Formation layer ALP Phase difference film Alignment film PL Protective layer PCIL Interlayer insulating film CE Common electrode GIL Scanning wiring insulating film PE Pixel electrode CH Contact hole SE Source wiring RF Reflecting electrode SL Signal wiring CFR Red color filter CFG Green color filter CFB Blue color filter CFH Color filter hole portion NEP Non-exposed portion RUL Rubbing roll RE ′ Pre-finished retardation layer LCAL Liquid crystal alignment direction REAL Retardation layer slow axis CONV Convex portion forming layer CEH Common electrode hole portion SCIL Uneven portion forming layer ORE1 First outer retardation layer ORE2 Second outer position Retardation layer

Claims (17)

A pair of substrates;
A liquid crystal layer sandwiched between the pair of substrates;
A plurality of pixels;
A reflective display portion and a transmissive display portion in each of the plurality of pixels;
Between one of the pair of substrates and the liquid crystal layer, a plurality of signal wirings, a plurality of scanning wirings formed to intersect the plurality of signal wirings, and an intersection of the signal wirings and the scanning wirings are formed. An active element, a pixel electrode, a common electrode, and a diffuse reflection part formed at a position corresponding to the reflective display part,
The diffusive reflecting portion has a concavo-convex forming layer in which a concave portion and a convex portion are formed, and a plurality of hole portions distributed so as to correspond to the convex portion of the concavo-convex forming layer, on the concave portion of the concavo-convex forming layer A liquid crystal display device comprising: the common electrode formed on the surface; and a reflective layer formed on the convex portion of the unevenness forming layer and the common electrode. The liquid crystal display device according to claim 1.
The liquid crystal display device in which the pixel electrode and the common electrode apply an electric field including a component parallel to the pair of substrate surfaces to the liquid crystal layer. The liquid crystal display device according to claim 1.
The liquid crystal display device wherein the alignment state of the liquid crystal layer when no electric field is applied is homogeneous alignment. The liquid crystal display device according to claim 1.
The liquid crystal display device, wherein the pixel electrode is a comb electrode. The liquid crystal display device according to claim 1.
A liquid crystal display device in which the common electrode and the reflective layer are supplied with the same potential. The liquid crystal display device according to claim 2.
A liquid crystal display device comprising a retardation plate disposed between the other substrate of the pair of substrates and the liquid crystal layer and only in the reflective display portion. The liquid crystal display device according to claim 6.
The liquid crystal layer of the reflective display unit functions as a quarter wave plate,
The retardation plate is a liquid crystal display device that functions as a half-wave plate. The liquid crystal display device according to claim 1.
The convex portions of the concave-convex forming layer are randomly arranged in a plane,
The liquid crystal display device in which the plurality of hole portions in the common electrode are distributed so as to correspond to the convex portions of the concave-convex forming layer . A pair of substrates;
A liquid crystal layer sandwiched between the pair of substrates;
A plurality of pixels;
A reflective display portion and a transmissive display portion in each of the plurality of pixels;
Between one of the pair of substrates and the liquid crystal layer, a plurality of signal wirings, a plurality of scanning wirings formed to intersect the plurality of signal wirings, and an intersection of the signal wirings and the scanning wirings are formed. An active element, a pixel electrode, a common electrode, and a diffuse reflection part formed at a position corresponding to the reflective display part,
The diffuse reflection portion includes a concavo-convex forming layer in which concave and convex portions are formed, a reflective layer formed on the concavo-convex forming layer, and a plurality of voids distributed so as to correspond to the convex portions of the concavo-convex forming layer. And a common electrode formed on the concave portion of the reflective layer with a hole . The liquid crystal display device according to claim 9.
The liquid crystal display device in which the pixel electrode and the common electrode apply an electric field including a component parallel to the pair of substrate surfaces to the liquid crystal layer. The liquid crystal display device according to claim 9.
The liquid crystal display device wherein the alignment state of the liquid crystal layer when no electric field is applied is homogeneous alignment. The liquid crystal display device according to claim 10.
The liquid crystal display device in which the common electrode and the reflective layer are supplied with power independently and have the same potential. The liquid crystal display device according to claim 10.
A liquid crystal display device comprising a retardation plate disposed between the other substrate of the pair of substrates and the liquid crystal layer and only in the reflective display portion. The liquid crystal display device according to claim 10.
The liquid crystal layer of the reflective display unit functions as a quarter wave plate,
The retardation plate is a liquid crystal display device that functions as a half-wave plate. The liquid crystal display device according to claim 9.
The convex portions of the concave-convex forming layer are randomly arranged in a plane,
The liquid crystal display device in which the plurality of hole portions in the common electrode are distributed so as to correspond to the convex portions of the concave-convex forming layer . A pair of substrates;
A liquid crystal layer sandwiched between the pair of substrates;
A plurality of pixels;
A reflective display portion and a transmissive display portion in each of the plurality of pixels;
Between one of the pair of substrates and the liquid crystal layer, a plurality of signal wirings, a plurality of scanning wirings formed to intersect the plurality of signal wirings, and an intersection of the signal wirings and the scanning wirings are formed. An active element formed, a pixel electrode, and a diffuse reflection part formed at a position corresponding to the reflective display part,
A common electrode is formed between the other substrate of the pair of substrates and the liquid crystal layer,
The diffusive reflecting portion has a concavo-convex forming layer in which a concave portion and a convex portion are formed, and a plurality of hole portions distributed so as to correspond to the convex portion of the concavo-convex forming layer, on the concave portion of the concavo-convex forming layer A liquid crystal display device comprising: the pixel electrode formed on the surface; and a reflective layer formed on the protrusion of the unevenness forming layer and on the pixel electrode. The liquid crystal display device according to claim 16.
A pair of polarizing plates sandwiching the pair of substrates;
A pair of retardation layers formed between one substrate of the pair of substrates and one polarizing plate of the pair of polarizing plates, and between the other substrate of the pair of substrates and the other polarizing plate of the pair of polarizing plates; A liquid crystal display device.

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